The notion of “fuzzy logic” is especially relevant: https://en.wikipedia.org/wiki/Fuzzy_logic
But this was exactly my point: scalars, regarded as 'singleton number's, don't include Booleans, because Booleans aren't numbers, singleton or otherwise. (Unless, again, you wish to regard them as belonging to the field with two elements.) Booleans can be coerced to numbers, but the way to do so, even if we agree that the two numbers are 0 and 1, is arbitrary—unless we require that certain algebraic identities hold, identities that indicate that the (usual) algebra of Booleans is not the (usual) algebra of real numbers.
It is a nitpick, to be sure; but (a) part of the point of types is to facilitate, and even automate, exactly this sort of nitpicking, and (b) it was in response to a nitpick, too.
> The notion of “fuzzy logic” is especially relevant: https://en.wikipedia.org/wiki/Fuzzy_logic
Agreed! It indicates that coercing Booleans to numbers suggests fruitful analogies, but, again, says to me that they are not actually numbers. (Once again, I point to their operators, which, from a computer-science as well as a mathematics point of view, are part of what a scalar, Boolean, or whatever is: https://en.wikipedia.org/wiki/Fuzzy_logic#Fuzzy_logic_operat... .) These indicate that perhaps one should think of Booleans as belonging to a continuum of values coming from a tropical-type structure (https://en.wikipedia.org/wiki/Tropical_geometry) rather than from a field as 'usual' scalars do.